Hybrid Automatic Retransmission request (HARQ) means an improved automatic retransmission request scheme where originally transmitted information and retransmitted information are decoded in combination to reduce the number of retransmission times according to an error occurring in initial data transmission. This HARQ scheme is used for an IEEE 802.16m system and other mobile communication system. Hereinafter, a method for allocating resources for uplink HARQ in an IEEE 802.16 system according to the related art will be described in brief.
A mobile station which has received an uplink basic assignment A-MAP information element (A-MAP IE) transmits sub-packets of HARQ data through resources allocated by the uplink basic assignment A-MAP IE. A base station attempts to decode a data burst, and if decoding is successfully performed, the base station transmits an acknowledgement (ACK) signal. However, if decoding is failed, the base station transmits a negative acknowledgement (NACK) to the mobile station. When the base station allocates resources to the mobile station for retransmission, it may not transmit the uplink basic assignment A-MAP. In this case, the base station allocates resources to the mobile station at the same position and size as those of a region allocated for a previous sub-packet at a subframe for retransmission. If the base station transmits the uplink basic assignment A-MAP to the mobile station to allocate resources for retransmission, it allocates resources to a region indicated by the corresponding A-MAP.
The mobile station which has received a NACK signal from the base station performs a retransmission procedure. If the mobile station fails to receive the uplink basic assignment A-MAP IE for HARQ data burst transmission through the retransmission procedure, it transmits next sub-packet to the base station through resources allocated during transmission of the last sub-packet having same ACID.
FIG. 1 is a diagram illustrating an example of an uplink HARQ procedure.
Referring to FIG. 1, the base station transmits an uplink basic assignment A-MAP IE to the mobile station, wherein the uplink basic assignment A-MAP IE indicates that uplink resources for data transmission of the mobile station have been allocated to a region A (S110). The mobile station which has received the uplink basic assignment A-MAP IE from the base station transmits sub-packets of HARQ burst through a resource region (region A) indicated by the corresponding IE (S120). If the base station fails to decode the packets due to an error occurring in the packets transmitted from the mobile station, it transmits a NACK signal to the mobile station to indicate the fact that an error has occurred in the transmitted packets (S130). Afterwards, the base station allocates to the mobile station resources having the same position and size as those of resources for transmission of a packet, in which the error has last occurred, without uplink basic assignment A-MAP, so that the mobile station retransmits the packet having an error at the designated time (S140).
If the mobile station receives the NACK signal from the base station but fails to receive the uplink basic assignment A-MAP IE for retransmission, it transmits retransmission packets using a region (region A) having the same position and size as those of a resource region last transmitted (S150). Then, the base station transmits an ACK signal to the mobile station in response to the retransmission packets if it normally receives the packets retransmitted from the mobile station through the allocated region A (S160). In this way, the base station can allocate the region having the same position and size as those of the resource region last transmitted from the mobile station, so that the mobile station can retransmit the packets having an error.
FIG. 2 is a diagram illustrating another example of an uplink HARQ procedure.
Referring to FIG. 2, in the same manner as FIG. 1, the base station transmits an uplink basic assignment A-MAP IE to the mobile station, wherein the uplink basic assignment A-MAP IE indicates that uplink resources for data transmission of the mobile station have been allocated to a region A (S210). The mobile station which has received the uplink basic assignment A-MAP IE from the base station transmits sub-packets of HARQ burst through a resource region (region A) indicated by the corresponding IE (S220). If the base station fails to decode the packets due to an error occurring in the packets transmitted from the mobile station, it transmits a NACK signal to the mobile station to indicate the fact that the error has occurred in the transmitted packets (S230).
Afterwards, the base station allocates the uplink basic assignment A-MAP IE to the mobile station to allocate resources having information (for example, different position or different size) different from that of resources most recently allocated for corresponding ACID, so that the mobile station retransmits the packets having an error at the designated time (S240). If the mobile station receives the NACK signal and the uplink basic assignment A-MAP IE for retransmission, it transmits retransmission packets to a resource region (region B) indicated by the corresponding A-MAP IE (S250).
Then, the base station transmits an ACK signal to the mobile station in response to the retransmission packets if it normally receives the packets retransmitted from the mobile station through the allocated region B (S260). In this way, the base station can allocate a new uplink resource region (region B) to the mobile station, so that the mobile station can retransmit the packets having an error.
In order to allocate resources for packet retransmission of the mobile station due to an error occurring in the packets transmitted from the mobile station, the base station can transmit the uplink basic assignment A-MAP IE to the mobile station. At this time, if the mobile station fails to decode the uplink basic assignment A-MAP IE, it transmits retransmission sub-packets to the base station through resources allocated to the sub-packet most recently transmitted for same ACID. In this case, ACID represents HARQ channel identifier.
Since the sub-packets transmitted by the mobile station are transmitted a wrong resource region, a problem occurs in that the sub-packets collide with packets transmitted from another mobile station. As a result, the base station fails to receive the packets transmitted from another mobile station. Also, the base station fails to receive retransmission packets from the corresponding mobile station through the resource region indicated by the uplink basic assignment A-MAP IE, and transmits NACK to the mobile station. Afterwards, if the base station allocates resources for retransmission without transmitting the uplink basic assignment A-MAP IE, the mobile station will continuously transmit retransmission packets using the wrong resource region. For this reason, waste of resources becomes serious.